This disclosure relates to a NAND flash memory device, and more specifically, to a NAND flash memory device that may detect errors during a copyback program, and a copyback program method thereof.
A NAND flash memory device is a semiconductor memory device that is used for storing data to read whenever it is required. The NAND flash memory is a nonvolatile memory device that is capable of maintaining data even when a power supply is cut off.
The NAND flash memory device includes a number of memory cells having a string structure. An organization of these memory cells is called a ‘cell array’. In the NAND flash memory device, the cell array is divided into a number of blocks and each block is divided into a number of pages. Each page includes a number of memory cells that share one word line.
The NAND flash memory device performs read and write operations by units of pages and an erase operation by units of blocks. The NAND flash memory device also supports “copyback” operations in addition to read, write, and erase operations. A copyback operation is one where data that is stored in a first page (or a source page) is moved to a second page (or a target page). Generally, copyback operations may include a copyback read operation, a copyback program operation, and a copyback program verify operation.
A copyback read operation reads data stored in a source page and stores it in a page buffer. A copyback program operation re-programs the data stored in the page buffer to the target page directly without reading the data out. A copyback program verify operation confirms whether data is correctly programmed to the target page. Using the copyback operations described above, the process of reading out data stored in the page buffer and loading the external data to the page buffer may be omitted to speed up the operation of the NAND flash memory device.
However, when copyback operations are carried out, a one-bit error may occur during the copyback read operation, and an additional one-bit error may occur during the copyback program operation and the copyback program verify operation. Therefore, two-bit errors may occur after the copyback operation. A memory controller in a general NAND flash memory device may correct only one-bit of error per page. Thus, copyback operations that cause two-bit errors in one page cannot be completely corrected.
Accordingly, one conventional method for preventing the occurrence of a two-bit error is to detect whether an error occurs in data stored to a page buffer from a source page by a copyback read operation. However, to stop the copyback operation in this manner and detect the error requires an additional time delay, so that the method has the undesirable tendency to decrease the high speed of the NAND flash memory.
Embodiments of the invention address these and other disadvantages of the conventional art.